1. Field of the Invention
This invention relates generally to tiltable chairs and more specifically to a novel base portion for tiltable chairs.
2. Description of the Prior Art
The tiltable chairs of the prior art usually comprise a seat and back portion as one unit, a chair control to control the tilting of the chair, and a base portion which includes a plurality of legs extending from a central portion radially outwards with wheels or casters on the peripheral ends of the legs. The legs of the chair converge to a central vertical post assembly which provides a link between the legs and the chair control itself. This central post assembly by its construction, allows the chair seat to swivel about the legs and also allows the seat of the chair to be raised or lowered according to the user's requirements.
The post assembly found in some chairs of the prior art consist essentially of a cylindrical threaded post, the upper portion of which is secured through a central opening to the chair control itself or to the underneath surface of the chair seat, and a tubular sleeve, the lower end of which is affixed to the inner ends of each leg and which fits over the cylindrical threaded post. A bell assembly is adjustably secured around the cylindrical post above the uppermost portion of the tubular sleeve.
The tubular sleeve of the prior art consists of a tube which is placed over the threaded post and the lower end of the tube includes vertical slots cut therein. The slots correspond to the number and position of the legs of the chair and the tube is constructed so that each leg of the chair fits into a corresponding slot. The tube and the legs are then welded together.
In most of these prior art devices, no means to align the tube in the vertical position relative to the post is provided. Once the sleeve is welded, it remains in that position. Thus, if the sleeve is not aligned vertically when it is welded, the assembly will be off centre. In these chairs of the prior art, it was therefore a painstakingly slow and cumbersome job to align the tube perfectly vertical relative to the cylindrical post prior to welding. If the tube was not aligned or if the fabricator did not take sufficient time and effort to align the tube, an assembly would be produced of inferior quality in both appearance and in utility.
In another embodiment of the prior art, an inner tubular sleeve was mounted directly on the threaded cylindrical post to effect vertical alignment of the post with the base portion. However, to achieve a secure fit with the post, the tolerances of the inner sleeve must be exact and usually, expensive C-drawn tubing was used. More recently, a nylon liner has been used to secure the inner tubular sleeve to the post. However, with these constructions, the inner tubular sleeve must still be of exact tolerances to create a tight fit and accordingly expensive tubing was still required.
With these devices of the prior art using the inner tubular sleeve, the inner ends of the legs of the chair were affixed to the lower portion of the sleeve by welding or similar means instead of relying on the outer sleeve to align the legs correctly.
The bell assembly of the prior art chairs was also a cumbersome device. The bell portion was inserted on the threaded cylindrical post and screwed downward to a point above the outer tubular sleeve. A washer was placed on the threaded post above the tubular sleeve. The bell assembly included a screw which was inserted through the vertical side wall of the bell and was screwed inwards below or underneath the washer and in contact with the threaded central post.
Thus, when the chair seat was rotated in one direction, (with the bell assembly stationary) the interior threaded post would rotate and screw itself upwards and raise the chair seat but only until the screw in the bell assembly engaged itself with the underneath portion of the washer. When the chair seat was rotated in the opposite direction, the central threaded post would screw itself downwards until the top portion of the washer engaged itself with the inner surface of the top horizontal surface of the bell.
In order to adjust the movement and the height of the chair seat and back, the screw must be loosened and the bell assembly raised. The washer was then adjusted either upwards or downwards and then the bell assembly was reassembled over the washer and the screw tightened. Also, to disassemble the assembly, the screw must be loosened and removed and the threaded post is screwed upwards and removed from the assembly.
A further example of the construction of the assembly of the prior art is shown in U.S. Pat. No. 3,185,430 granted on May 25, 1965 to C. H. M. Bernard. This device utilizes a helical spring and a threaded post to allow the height of the chair seat to be adjusted.
The devices of the prior art have many problems associated therewith. In particular, the assemblies have been rather complicated to manufacture and thus add a considerable cost to the production of the chair. The inclusion of the screw in the assembly and its mode of operation necessitates tools for assembly and disassembly which does not allow for quick and efficient adjustment by the user of the chair. The adjustment of the assembly becomes a complicated procedure which does not lend itself to easy serviceability.
Also, the tubular sleeve of the base assembly is not always mounted in the vertical position when the chair is assembled. This can result from poor welding techniques or not taking sufficient care in the assembly stage. It is particularly difficult to align the tube vertically with respect to the post and hold it there during welding without additional expensive equipment.
Thus, when the assemblies are made in the prior art, the tubular sleeve is not always vertically aligned which detracts significantly from the operation and appearance of the chair.
Also, when an inner tubular sleeve was used with the devices of the prior art, expensive C-drawn tubing was always required to achieve a good fit with the threaded post, thereby increasing the cost of the manufacture of the chairs.